1. Field of the Invention
This invention relates to devices for producing forces on a missile in flight and, more particularly, to a lateral thruster used to produce a lateral force which can be controlled in magnitude and direction and can be used to translate the missile laterally and/or provide steering.
2. Description of the Related Art
One of the basic goals of the technology of missile flight is to improve both the maneuverability of the missile and its response time. In discussing possible improvements it is appropriate to consider a typical missile that uses aerodynamic forces for both steering and maneuvering. The steering forces are those that are used to control the pitch, yaw, and roll of a missile.
The maneuverability of a missile is related to its ability to change its flight path. Since lateral forces cause a missile to change its flight path, the maneuverability of a missile is related to its ability to develop lateral forces. Aerodynamic lateral forces are created on a missile when the missile is made to fly at what is known as an aerodynamic angle of attack, i.e., at an angle relative to its flight path. This is achieved by applying steering forces that are typically created by deflecting control surfaces that are forward or aft of the missile center of gravity.
Aerodynamic lateral forces due to angle of attack and aerodynamic steering forces decrease dramatically with missile velocity and with altitude. These forces also reach maxima with aerodynamic angle of attack and with control surface deflection angle. Control surfaces are often not very effective when the missile is at a high aerodynamic angle of attack.
It would be a great boon to the technology of missile flight control if there existed thrusters that could produce lateral forces and steering forces that were essentially independent of missile aerodynamic angle of attack, missile velocity and altitude, and, in the case of steering forces, independent of control surface deflection angles.
The response time of a missile is a measure of how fast it can execute a maneuver, which is related to how rapidly lateral forces can be developed. For a typical missile a maneuver sequence starts with the deflection of control surfaces. This provides steering forces which cause the missile to pitch or yaw to an aerodynamic angle of attack which produces the necessary lateral forces. It would lead to a great improvement in missile response time if lateral forces could be developed without any delay for the missile to develop an aerodynamic angle of attack.
Some examples of the related art are discussed below.
U.S Pat. No. 3,446,436 to Desjardins et al discloses a rocket thrust nozzle system in three embodiments. The first is directed to a main rocket motor with four secondary motors fixedly attached around it. The forward longitudinal thrust of the main rocket motor is deflected by means of secondary injection to provide steering forces to the missile. The steering forces end when the main motor thrust ends. The secondary motors provide longitudinal thrust only, with no provision to provide steering forces. Their thrust is turned by use of canted nozzles to impinge on a rearwardly convergent cone. The first embodiment disclosed provides what is generally known as thrust vector control to the forward longitudinal thrust of a main rocket motor and provides additional longitudinal thrust by means of what are generally known as strap-on boosters.
In the second embodiment the canted nozzles on the secondary motors have been made rotatable to provide steering forces, including roll control, to the missile. The nozzles rotate while the rocket motor casings remain fixed to the main rocket. The second embodiment provides what is generally known as thrust vector control to the forward longitudinal thrust of what are generally known as strap-on boosters.
In the third embodiment the rotatable nozzles have been inserted into the base of the main motor casing with the intent of providing steering forces to the forward longitudinal thrust of the main motor. This approach is generally described as thrust vector control by means of multiple nozzles.
The secondary motors can only be located at the aft end of a missile, clearly aft of the missile center of gravity. At this location they can only provide steering forces that are opposite to the direction desired for the missile. In addition, the secondary motors can only be located generally external to the missile body. The nozzles on the secondary motors rotate with the motors remaining fixed.
European patent application No. 0,069,440 by Young is directed toward a gas thruster device that utilizes a pair of rotatable nozzle assemblies for discharging gas to control the flight of a missile by providing pitch, yaw, and roll steering forces. When the propellant ignites in the combustion chamber, the gases travel rapidly through the duct leading to the nozzle. At the end of the duct the gases are turned through 90.degree. before being expelled through the nozzle.
U.S. Pat. No. 3,286,956 to Nitikman relates to an integrated control system with a common actuation means for reaction or reaction plus aerodynamic control of a multi-phase or multi-stage rocket vehicle. A plurality of movable aerodynamic control surfaces extend fore and aft of a missile body adjacent to the exterior surface thereof. Each of the surfaces has a relatively flat, pointed forward edge and a relatively thick, blunt trailing edge. A rocket nozzle mounted within each of the control surfaces has its mouth directed rearwardly along the blunt edge. A rocket motor mounted within the missile has a single outlet to which a manifold is attached.
U.S Pat. No. 2,552,359 to Winslow, Reissue 23,936, discloses a method for effecting attitude control of aircraft, and particularly to a method by the pilot of directing the aircraft attitude, including means for automatic control of angular acceleration of the aircraft to bring about the attitude directed by the pilot. A mechanical means for accomplishing directional control consists of an arrangement of four thrust-producing units which assist in the angular movement of the aircraft about any one or combination of its three principal axes and provide forces of thrust as a means of propulsion.
U.S. Pat. No. 2,822,755 to Edwards et al describes a mechanism for causing a missile to maintain a desired heading regardless of the cooperation of external forces that would cause deviation from its intended path. A plurality of jets uniformly spaced about the periphery of a rocket are provided which derive their gases from that propelling the rocket, the jets being selectively controlled by a gyroscope-actuated mechanism for rotating the rocket about its center of gravity, thus maintaining the rocket on, or parallel to, its intended heading.
U.S. Pat. No. 2,938,459 to McGraw et al relates to a gimbal bearing or universal type bearing for carrying a thrust load between two members. The gimbal bearing is designed for use in guided missiles as a means of permitting the universal movement of rocket engines therein and, at the same time during flight, to receive their thrust.
U.S. Pat. No. 2,995,319 to Kershner et al relates to a pre-boost control device for an aerial missile which utilizes a plurality of jet reaction nozzles to control the roll, pitch, and yaw attitude of a missile. Four small reaction nozzles are mounted at the rear of the missile and carried in bearings in such a way that the direction of pointing of their jets can be altered. Hot high-pressure gas is supplied to the nozzles by the products of combustion of a propellant housed in a chamber common to all of the nozzles. The nozzles are mechanically linked to the missile tail fins in such a way that deflection of the tail fin rotates the nozzle attached to that fin to provide a turning moment on the missile in the same direction as would result from the aerodynamic moment of the deflected tail fin.
U.S Pat. No. 3,057,581 to Tumavicus discloses a rocket vectoring arrangement comprising a plurality of rockets or nozzles mounted at substantial distances from a vehicle axis, such that when the axes of the several nozzles or rockets are parallel to the vehicle axis, the discharge ends of the nozzle are spaced apart radially so that vectoring of some of the nozzles in any direction may occur.
U.S. Pat. No. 3,070,329 to Hasbrouck is directed toward the use of a plurality of independently movable steering rockets by which to impart to a main rocket or vehicle a steering thrust at an acute angle to the line of thrust of the main propulsive nozzle. The steering rockets are arranged external to the vehicle in such a way that the resulting steering thrust may be at any angle desired, with the steering rockets normally extending axially and supplementing the thrust of the main nozzle.
U.S. Pat. No. 3,115,318 to Caillette relates to the maintenance of any desired direction of flight of rocket or jet propelled flying bodies and more particularly to aircraft including pilotless missiles utilizing jet thrust for flying both vertically and horizontally. A flying body is provided with any suitable number of angularly adjustable thrust-producing units for the dual purpose of providing force of thrust as a means of propulsion and as a means of constantly maintaining any desired direction of flight.
U.S. Pat. No. 3,180,0B4 to Meeks is directed toward a thrust device comprising a spherical container made of lightweight metal and filled with a propellant gas under relatively high pressure. The container is formed with diametrically aligned hubs forming coaxially extending cylindrical openings. A valve unit is slidably fitted in the openings in the hubs to form a complete self-contained thrustor unit. The disclosed construction enables the container to expand and contract in accordance with temperature and pressure differentials in such a way that the valve unit is not subject to strain resulting from distortion of the container.
U.S. Pat. No. 3,188,024 to Schneider is directed toward an aircraft steering and propulsion unit utilizing pivotally mounted reaction motors so that the direction of the exhaust of those motors can be directed to intersect and thereby increase the propulsion of the craft in rarefied atmosphere. The pivotally mounted reaction engines can also be used to provide a deceleration effect on a spacecraft as it re-enters the atmosphere.
U.S. Pat. No. 3,249,325 to Forehand discloses a missile guidance system including combined steering and propulsive means for steering missiles upon a predetermined trajectory by a gyroscope control means for adjustably positioning combined steering and propulsion nozzles carried by the missile.
None of the patents or patent applications described above is directed to a configuration of thruster motors which provide mainly lateral thrust; which can be located to act aft of, forward of, or at the missile center of gravity; which can be buried in the missile body to reduce aerodynamic drag and accommodate launching from canister-type launchers; and which operate completely independently of the forward longitudinal thrust of the main rocket motor without using secondary injection methods to alter the direction of thrust. None discloses an arrangement of rotatable thruster motors with integral nozzles to eliminate sealing problems and thrust plate or ring friction forces, and with drive assemblies which are well protected from hot exhaust gases.